The present invention relates to an internal-combustion engine having a gas inlet port that is subdivided into at least two partial ports by a partitioning wall extending over at least a portion of the length of the port.
In piston-type internal-combustion engines, it is known from, for example, WO 95/17589 and DE-A-198 03 867, to subdivide at least the cylinder port that is connected to the gas-intake valve of each cylinder into two partial ports, over at least part of the port length, using at least one partitioning wall. A control device is provided at the beginning of the partitioning wall, when seen in the flow direction, for at least one of the two partial ports. This device can influence the volume flow that flows through this partial port. Thus, it is possible to purposefully guide the flow through at least one of the partial ports and to a segment of the valve-gap region of the gas-intake valve, and to change the distribution of the air mass or charge mass flowing into the cylinder by throttling the other partial current. Because the distribution of the charge mass via the valve gap dictates the creation of turbulence in the cylinder, the throttling of at least one of the partial ports can control the turbulence formation and intensity in the cylinder. At the same time, it is possible to influence the extent of the mixing of the different charge components. Hence, the mass distribution onto the upper and lower valve-gap regions can be influenced. If a larger proportion of the mass is conducted through the upper valve-gap region, a tumbling effect is created in the cylinder. This tumbling can have a positive effect on combustion and, if desired, permits a stable stratification between the air and fuel and/or the exhaust gas. If the lower partial port is closed, the turbulence also effects a favorable combustion behavior with low engine loads (partial load). With a full load, however, no intensive turbulence is supposed to be generatedxe2x80x94in other words, both partial ports should remain open.
For structural reasons, the first partial port, which is preferably the upper one, is connected to the fuel supply such that, for example, a fuel-injection nozzle discharges into this partial port. Depending on the operating mode, if the lower partial port is closed or slightly open, the fuel-air mixture flows through the upper, first partial port and is predominantly guided to the upper valve-gap region. The charge mass supplied to the lower valve-gap region is increased in proportion to the increase of the supply of air or exhaust gas from the exhaust-gas return via the second, lower partial port, so the turbulence formation in the cylinder is reduced corresponding to the increase in the gas flow through the second partial port. If the distribution of the charge mass being conducted through the gas intake onto the two partial ports is controlled, this can infinitely variably influence the intensity of the tumbling. This is also a function of a piston-type internal-combustion engine with direct fuel injection.
A corresponding structural embodiment of the port partition, and/or the selection of the time of the fuel supply (injection time), can have a positive impact on the mixing of the fuel-air mixture or the exhaust gas-fuel-air mixture. The mixture can be intensively mixed (homogeneous mixture) or distinctly stratified. This construction further permits the introduction of exhaust gas into at least one partial port and, depending on the throttling of the other partial port, a more or less defined stratification of the exhaust gas-air-fuel mixture. In an arrangement involving a plurality of intake valves per cylinder, it is possible to provide a common intake region for all of the intake valves, in which the partitioning wall that subdivides the intake port ends, or to allow each intake valve of a cylinder to exert its own influence through a corresponding division into two parallel ports, beginning from a common port part. In the latter case, the partitioning wall effecting a corresponding division extends from the common port area into the region of the two parallel ports, so the end of the partitioning wall can also be brought closely to the valve gap of the relevant intake valve.
It is also known from WO 95/17589 to cast the partitioning wall with corresponding casting cores in the production of the cylinder head, or to place a corresponding structural element comprising a different material, such as a stamped steel sheet, into the casting mold and embed it into the cylinder head.
It is the object of the invention to improve a piston-type internal-combustion engine of the aforementioned type, with respect to the embodiment of its cylinder ports, particularly the gas intake ports.
In accordance with the invention, the above object generally is achieved with a piston-type internal-combustion engine having at least one cylinder port, which essentially discharges into a cylinder via at least one throughgoing opening, per cylinder. This port is divided, at least over a part of its length, into at least two partial ports by at least one partitioning wall that has a profile with flow channels extending in the flow direction on one surface of the wall. It is preferable for the divisional plane that is defined by the partitioning wall to be oriented essentially transversely to the cylinder axis.
In contrast to the known, smooth-surface embodiment of the partitioning walls, the profile with the flow channels in accordance with the invention offers the option of also profiling the mass flow transversely to its flow direction, that is, to create xe2x80x9cstrandsxe2x80x9d with a higher mass-flow density, so the mass flow traversing the relevant partial port is shaped accordingly. With two essentially parallel troughs or flow channels that are disposed at least in the vicinity of the throughgoing opening, for example, it is possible to provide two partial flows that have an increased mass flow, particularly for the upper partial port, and to guide these flows past both sides of the valve stem, which passes through the end region of the intake port, in order to avoid turbulence or an undesired diversion of the mass flow toward the edge. With a corresponding embodiment of the trough or flow channel shape, it is also possible for the main component of the mass flow to be diverted more strongly toward the center of the cylinder, or toward the cylinder wall, depending on the embodiment of the combustion chamber.
While it is possible in principle to provide this type of flow channel shape with respect to the two partial ports, for example, in the form of a wavy cross-section of the partitioning wall, it can be advantageous to allocate the trough shape to only one partial port, for example the upper partial port, while the partitioning wall for the other partial port has a level or flat surface.
A wavy cross-sectional shape of the partitioning wall is advantageous both for a partitioning wall that is cast with the cylinder head and for a partitioning wall that is cast as a separate component, particularly as a separate piece of sheet steel, because the changes in spacing that occur due to thermal expansions caused by different temperature levels can be readily accommodated, and ruptures in the partitioning wall or a loosening of the partitioning wall from the casting material can be avoided. The concept of the invention is not, however, limited to a cast or embedded partitioning wall. A partitioning wall that is inserted later, for example as a steel sheet, into cast slots in the port side wall is technically advantageous, but also solves structural problems that are caused by different thermal expansions.
The invention is described in detail below using schematic drawings of exemplary embodiments.